Transporting epithelia function in widely differing capacities ranging from involvement in exocrine gland function to homeostatic control of body fluids. The objectives of the proposed research are to explore some of the similarities and differences between secretory and reabsorptive tissues as reflected in their correlative physiological and morphological transport properties. We will continue to use the avian salt gland as a model secretory tissue and will employ a newly devised preparation of dissociated cells from the gland. Some of the basic mechanisms involved in ion uptake and extrusion, and the relationships of these processes to cellular respiration, sensitivity to transport inhibitors, and responsiveness to cholinergic secretagogues will be revealed by unidirectional ion flux studies in isolated cells and in tissue slices. Aspects of the coupling of cholinergic stimulation to secretory responses of cells will also be examined. These data, together with data on the distribution of Na ion pumps and on freeze fracture analyses of occluding junctions in salt glands and other secretory epithelia, will be related to recent hypothetical models for secretory salt transport. Comparative studies in mammalian kidney and salt gland epithelia will be carried out to compare and contrast physiological and morphological correlates to cell volume regulation, and the relative sensitivities of cellular transport processes and respiration to diuretics. The localization of Na ion-K ion-ATPase in kidney medulla from several mammalian species will be demonstrated by cytochemical and autoradiographic techniques and the distribution of the enzyme will be correlated with species-specific differences in structural and physiological characteristics of individual nephron segments.